Did a clean install today, just finished configuring it a few minutes ago. It's still too soon to tell if there's any drawback under the hood, but the first impressions of its behaviour are positive. Much better UI, with all tools centralized in a single location, instead of being separated like before, and drastically reduced memory usage. A couple of things seems to be missing in comparison with version 4.8, namely URL blocking (let's be fair, nobody used it), and indications on the system tray when the program is getting updates. IMO this is a big loss, because notification boxes are fairly invasive for such info.
BTW, for the fans of avast! voiceovers, those are still present, and thinking in the sanity of the rest of the world, Alwil has provided us with simple notifications sounds as well.